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Correct Answer: all will reduce
fehling's solution is a chemical reagent used to differentiate between water-soluble carbohydrate and ketone functional groups, and as a test for monosaccharides. it is typically made by mixing two solutions, fehling's "a" and fehling's "b". fehling's a contains a deep blue aqueous solution of copper(ii) sulfate, and fehling's b contains potassium sodium tartrate (rochelle salt) in a strong base of sodium hydroxide. when these two solutions are mixed together in equal amounts, they form a complex, alkaline solution.
the test for reducing sugars with fehling's solution is based on the reduction of the complexed copper(ii) ion (cu^2+) to copper(i) oxide (cu2o), which is a red precipitate. aldehyde groups (-cho) and alpha-hydroxy ketones can reduce the copper(ii) ion to copper(i) oxide under the alkaline conditions of the test. therefore, compounds containing these functional groups will give a positive fehling's test.
the compounds mentioned in the question are formic acid, ethanal, and 2-methylpropanal.
1. **formic acid (hcooh)**: formic acid is the simplest carboxylic acid and contains a -cooh group. unlike most other carboxylic acids, formic acid can also act as a reducing agent because it can readily donate a hydrogen atom, effectively reducing other substances. in the context of fehling's solution, formic acid can reduce copper(ii) to copper(i), resulting in a positive test.
2. **ethanal (acetaldehyde, ch3cho)**: ethanal is an aldehyde with the structure ch3cho. the aldehyde group (-cho) is known for its reducing properties, as the hydrogen atom attached to the carbonyl carbon is easily oxidizable. therefore, ethanal will also reduce copper(ii) in fehling's solution to copper(i) oxide, giving a positive result.
3. **2-methylpropanal (isobutyraldehyde, (ch3)2chcho)**: this compound is another aldehyde, similar to ethanal but with an additional methyl group. like ethanal, the aldehyde group in 2-methylpropanal can reduce the copper(ii) ion in fehling's solution to copper(i) oxide. thus, it will also give a positive result in the fehling's test.
in conclusion, all the mentioned substances have the capability to reduce fehling's solution either through their aldehyde group or, in the case of formic acid, through its unique properties as a carboxylic acid that can also act as a reducing agent. thus, the correct answer to the question is that all listed substances will reduce fehling's solution.
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